Shift device for hydraulic control system for automatic transmission

Abstract

A hydraulic control system comprises first and second shift valves which cooperate with each other to effect a shift between two gear ratios. The first shift valve has a port and two different pressure acting areas which are exposed to pressure from the port depending upon downshift and upshift states of the first shift valve, respectively. The second shift valve effects communication between signal pressure generating means and the port of the first shift valve when the second shift valve is in one of two states to deliver the signal pressure to the port of the first shift valve. A kickdown pressure generating means delivers a kickdown pressure to the first shift valve.

What is claimed is: 
     
       1. A hydraulic control system for an automatic transmission for a motor vehicle having an internal combustion engine with a throttle valve, the automatic transmission including at least one forward drive gear ratio lower than at least one other forward drive gear ratio, the transmission including a plurality of friction elements including a friction element for contributing to shifting between the one forward drive gear ratio and the one other forward drive gear ratio, the hydraulic control system comprising: a first shift valve having a housing with a wall portion defining a valve bore;   a second shift valve having a housing with a wall portion defining a valve bore;   line pressure generating means for delivering a line pressure to said first shift valve;   first signal pressure generating means for delivering a first signal pressure to said first and second shift valves;   second signal pressure generating means for delivering a second signal pressure to said first and second shift valves;   kickdown pressure generating means for delivering a kickdown pressure to said first shift valve;   said first shift valve including a line pressure inlet port, a line pressure outlet port, a first signal pressure port, a second signal pressure port receiving said second signal pressure and a kickdown pressure port receiving kickdown pressure, said line pressure inlet and outlet ports, said first signal pressure and second signal pressure ports, and said kickdown pressure port being disposed in said wall portion of said first shift valve;   said line pressure inlet and outlet ports being selectively communicating with each other;   said second shift valve including a signal pressure inlet port receiving said second signal pressure, and a signal pressure outlet port communicating with said first signal pressure port of said first shift valve, said signal pressure inlet and signal pressure outlet ports being disposed in said wall portion of said second shift valve;   said signal pressure inlet and outlet ports of said second shift valve selectively communicating with each other;   said first shift valve including a valve element movable within said valve bore of said first shift valve between a downshift position and an upshift position;   said valve element of said first shift valve including means for effecting communication between said line pressure inlet and outlet ports when said valve element of said first shift valve is in the upshift position to, in turn, effect communication between said line pressure generating means and the friction element to establish the one forward drive gear ratio, said valve element of said first shift valve also including means for blocking communication between said line pressure inlet and outlet ports when said valve element is in the downshift position to, in turn, block communication between said line pressure generating means and the friction element;   said valve element of said first shift valve including a first pressure acting area exposed to pressure from said first signal pressure port of said first shift valve when said valve element of said first shift valve is in the downshift position, a second pressure acting area exposed to second signal pressure from said second signal pressure port of said first shift valve when said valve element of said first shift valve is in the downshift position, said second pressure acting area being exposed to pressure from said first signal pressure port of said first shift valve when said valve element of said first shift valve is in the upshift position, and a third pressure acting area exposed to kickdown pressure from said kickdown pressure port when said valve element of said first shift valve is in any one of the downshift and upshift positions, said first pressure acting area being exposed to kickdown pressure from said kickdown pressure port when said valve element of said first shift valve is in the upshift position, said valve element of said first shift valve having an end pressure acting area exposed to said first signal pressure from said first signal pressure generating means when said valve element of said first shift valve is in any one of the downshift and upshift positions,   said second shift valve including a valve element movable in said valve bore of said second shift valve between first and second positions;   said valve element of said second shift valve including means for effecting communication between said signal pressure inlet and signal pressure outlet ports of said second shift valve when said valve element of said second shift valve is in the first position to, in turn, effect communication between said second signal pressure generating means and said first signal pressure port of said first shift valve, said valve element of said second shift valve further including means for blocking communication between said signal pressure inlet and signal pressure outlet ports of said second shift valve when said valve element of said second shift valve is in the second position to, in turn, block communication between said second signal pressure generating means and said first signal pressure port of said first shift valve;   said valve element of said second shift valve further including a first pressure acting area exposed to second signal pressure from said signal pressure inlet port of said second shift valve when said valve element of said second shift valve is in the first position and a second pressure acting area exposed to second signal pressure from said signal pressure inlet port when said valve element of said second shift valve is in the second position, said valve element of said second shift valve having an end pressure acting area exposed to said first signal pressure from said first signal pressure generating means.   
     
     
       2. A hydraulic control system as claimed in claim 1, wherein said first signal pressure is a governor pressure indicative of a vehicle speed of the motor vehicle, and said second signal pressure is a throttle modulator pressure indicative of an opening degree of the throttle valve, said throttle modulator pressure being the same magnitude of the kickdown pressure under a kickdown condition. 
     
     
       3. A hydraulic control system as claimed in claim 1 or 2, wherein said third pressure acting area receiving the kickdown pressure from said kickdown pressure port changes in area depending upon one of the downshift and upshift positions of said valve element of said first shift valve. 
     
     
       4. A hydraulic control system as claimed in claim 1 or 2, wherein said valve element of said first shift valve is a valve spool having thereon first, second, and third circumferential lands which are larger in diameter in this sequence and which are axially spaced from each other, said valve element of said first shift valve including at least one circumferential groove between each two adjacent lands, said first pressure acting area of said valve element of said first shift valve includes a circumferential groove between said first and second circumferential lands, said second pressure acting area of said valve element of said first shift valve includes a circumferential groove between said second and third circumferential lands, said third pressure acting area includes said first land, and said third land blocks said second signal pressure port when said valve element of said first shift valve is in the upshift position. 
     
     
       5. A hydraulic control system as claimed in claim 4, wherein said valve spool includes a fourth land, said valve element of said first shift valve including a circumferential groove between said third and fourth circumferential lands, and said means for effecting communication between said line pressure inlet and outlet ports including the groove between said third and fourth circumferential lands, said means for blocking communication between said signal pressure inlet and outlet ports includes said third circumferential land. 
     
     
       6. A hydraulic control system as claimed in claim 5, wherein said first shift valve includes a third signal pressure port receiving said first signal pressure, said valve element of said first shift valve includes a fourth pressure acting area exposed to first signal pressure from said third signal pressure port when said valve element of said first shift valve is in the downshift position. 
     
     
       7. A hydraulic control system as claimed in claim 6, wherein said valve spool of said first shift valve includes a fifth land larger in diameter than said fourth land, said valve element of said first shift valve including a groove between said fifth and sixth lands, said fourth pressure acting area including the groove between said fourth and fifth lands, said fifth land of said valve spool of said first shift valve blocking said third signal pressure port of said first shift valve when said valve element of said first shift valve is in the upshift position. 
     
     
       8. A hydraulic control system as claimed in claim 7, wherein said valve element of said second shift valve is a valve spool having thereon first, second and third circumferential lands which are larger in diameter in this sequence and which are axially spaced from each other, said valve element of said second shift valve including at least one circumferential groove between each two adjacent lands; wherein said first pressure acting area of said valve element of said second shift valve includes a groove between said first and second lands of said valve spool of said second shift valve and a groove between said second and third lands of said valve spool of said second shift valve; and   wherein said second pressure acting area of said valve element of said second shift valve includes the groove between said second and third lands of said valve spool of said second shift valve.